In our daily life, various electronic apparatuses and their accessories, such as power adapters, connectors, power supplies, plugs or sockets, etc., are widely used. Since the internal electronic elements and circuits of these electronic apparatuses or accessories need to be appropriately isolated and protected, they are covered by cases to avoid the contact with the external environment. The assembly structure of the case and the assembling method therefor will indirectly influence the appearances and the electrical properties of the electronic apparatuses or accessories, so it is important to design an appropriate assembly structure of the case and the assembling method therefor.
Please refer to FIG. 1, which is a schematic view showing the assembly structure of a conventional case. As shown in FIG. 1, the assembly structure of the conventional case is composed of an upper case 1 and a lower case 2. The upper case 1 has a connection portion 11 including a first protrusion 112, a first trench 113 and a second protrusion 114 arranged from the external side 110 to the internal side 111 of the upper case 1. The lower case 2 also has a connection portion 21 including a first cavity 212, a first protrusion 213 and a second cavity 214 arranged from the external side 210 to the internal side 211 of the lower case 2 and opposite to the first protrusion 112, the first trench 113 and the second protrusion 114 of the upper case 1, respectively. In addition, the first protrusion 213 of the lower case 2 has a protruding rib 215 thereon, and the width of the first protrusion 213 of the lower case 2 is slightly smaller than that of the first trench 113 of the upper case 1. Thereby, when the upper case 1 and the lower case 2 are assembled, the first protrusion 213 of the lower case 2 can be inserted into the first trench 113 of the upper case 1.
Please refer to FIGS. 2(a)–(b), which schematically show the assembling manner of the structure in FIG. 1. As shown in FIG. 2(a), when the upper case 1 and the lower case 2 are going to be assembled, the first protrusion 112, the first trench 113 and the second protrusion 114 of the upper case 1 are first put in opposition to the first cavity 212, the first protrusion 213 and the second cavity 214 of the lower case 2, respectively. Then, with the ultrasound principle, the ultrasound generated by the horn of an ultrasonic plastic welding machine produces ultra-frequent sonic vibration on the cases, so that the upper case 1 and the lower case 2 rub against each other violently and thus the protruding rib 215 on the first protrusion 213 of the lower case 2 can be welded into the inner wall of the first trench 113 of the upper case 1 in a very short time, as shown in FIG. 2(b), so as to achieve the purpose of assembling the upper case 1 and the lower case 2.
However, no matter adopting what assembly structure of the case, the upper case 1 and the lower case 2 are produced by plastic injection molding. As known by one skilled in the art, the products made from plastic injection molding usually have disadvantages of fracture, shade or flow mark, lack of gloss, or deformation and so on. In which, the reason that causes the formation of flow mark on the product of plastic injection molding includes: the material is not welded well; the temperature of the mode is too low; the injection rate is too fast or too slow; the injection pressure is too high or too low; or the thickness difference on the cross-section of the product is too large. The reason that causes the formation of shade on the product is the wall thickness of the connection portion of the case is uneven. Since the shade or flow mark will influence the appearance of the assembled case, how to reduce the formation of shade or flow mark is an important issue.
Please refer to FIG. 1 again. From the external side 110 to the internal side 111 of the upper case 1 of the assembly structure of the conventional case, due to the level difference between the first protrusion 112 and the first trench 113, the thickness difference on the cross-section of the connection portion 11 of the upper case 1 is too large or the wall thickness of the connection portion 11 of the upper case 1 is uneven. Therefore, after the upper case 1 is injection molded, the shade 120 or flow mark will be formed on the external side 110 of the connection portion 11. The bigger the level difference between the first protrusion 112 and the first trench 113 is, the bigger the range of the shade 120 or flow mark is, so that when the upper case 1 and the lower case 2 are assembled, the obvious shade 120 or flow mark will be formed on the external side of the case and the surface of the case will be less smooth. In addition, after the upper case 1 and the lower case 2 are assembled, the creepage distance formed between the connection portions 11 and 12 is not long enough, so the electric leakage may occur, which indirectly influence the electric properties of the electronic apparatus or its accessory.
Therefore, it is needed to provide an assembly structure of a case and the assembling method therefor which can decrease the formation of shade or flow mark on the case and increase the creepage distance of the assembled case to overcome the disadvantages of the prior art as described above.